The invention relates to a process for preparing triethylenetetramine (TETA) by hydrogenation of ethylenediaminediacetonitrile (EDDN) over a catalyst, wherein EDDN is prepared by reaction of ethylenediamine (EDA) with formaldehyde and hydrocyanic acid (HCN). If appropriate, EDDN can also be present as constituent of an amino nitrile mixture which additionally comprises ethylenediaminemonoacetonitrile (EDMN). Diethylenetriaminemonoacetonitrile (DETMN) or diethylenetriaminediacetonitrile (DETDN) can additionally be comprised in the amino nitrile mixture as a result of recirculation of diethylenetriamine (DETA) obtained, if appropriate, in the hydrogenation. Hydrogenation of these further amino nitriles additionally gives tetraethylenepentamine (TEPA).
It is generally known that aliphatic nitriles, which may optionally be additionally substituted by further functional groups, can be hydrogenated in the presence of catalysts to form the corresponding amines. As indicated below, such hydrogenation processes are also known for various amino nitriles for the purpose of preparing some amines. However, up to now it has not been disclosed anywhere that TETA can also be prepared from the amino nitrile EDDN or, if appropriate, from an amino nitrile mixture comprising EDDN and EDMN by direct hydrogenation of the amino nitrile. However, the previously known processes for preparing TETA are, as indicated below, associated with disadvantages.
The prior art describes numerous processes for the hydrogenation of the α-amino nitriles aminoacetonitrile (AAN) and iminodiacetonitrile (IDAN) or of β-amino nitriles. Thus, it is known that the hydrogenation of n-amino nitriles generally proceeds without problems while the hydrogenation of α-amino nitriles is associated with the occurrence of numerous disadvantages such as hydrogenolysis of the C—CN bond or the R2N—C bond. “Handbook of Heterogeneous Catalytic Hydrogenation for Organic Synthesis, pages 213 to 215” indicates the problems of hydrogenation of α-amino nitriles for α-alkylamino nitriles or cyclic α-amino nitriles compared to β-amino nitriles. The known stability problems associated with α-amino nitriles are presumably the main reason why only the hydrogenation of the α-amino nitriles AAN or IDAN to EDA (ethylenediamine) or DETA (diethylenetriamine) has been described in detail to date. EDA or DETA are prepared industrially by the EDC or MEA processes described below. However, a corresponding hydrogenation is not known for higher α-amino nitriles.
DE-A 3 003 729 describes a process for the hydrogenation of aliphatic nitrites, alkyleneoxy nitrites and alkyleneamino nitrites to primary amines over a cobalt or ruthenium catalyst in the presence of a solvent system. The solvent system used comprises water and ammonia together with an ether or polyether. The alkyleneamino nitriles or alkyleneoxy nitriles which can be used as starting materials are in each case defined by means of complex general formulae. As specific compounds or examples which can be hydrogenated to the corresponding diamine, mention is made of, inter alia, ethylenediaminedipropionitrile (EDDPN; also referred to as N,N′-bis(cyanoethyl)-ethylenediamine) and 3,3′-(ethylenedioxy)dipropionitrile. DE-A 3 003 729 discloses, on the other hand, no suggestion as to the use of individual compounds of EDA derivatives having cyanomethyl substituents, e.g. EDDN or EDMN. In addition, the latter does not come under the general definition of alkyleneamino nitrites according to this document.
EP-A 0 382 508 describes a process for the batchwise preparation of acyclic, aliphatic polyamines by hydrogenation of acyclic, aliphatic polynitriles in the liquid phase over Raney cobalt catalysts, preferably in the presence of anhydrous ammonia. Here, a polynitrile solution is fed into a reaction zone comprising the Raney cobalt catalyst in an essentially oxygen-free atmosphere. During the entire reaction time, the polynitrile solution is fed in at a rate which is no greater than the maximum rate at which the polynitrile reacts with the hydrogen in the reaction zone. This process makes it possible to prepare polyamines from polynitriles such as iminodiacetonitrile (IDAN), nitrilotriacetonitrile (NTAN), ethylenediaminetetraacetonitrile (EDTN) or further compounds having 2 or more cyano groups which are not specified in more detail. The direct hydrogenation product of IDAN is diethylenetriamine (DETA).
EP-A 212 986 relates to a further process in which the same aliphatic polynitriles as in EP-A 0 382 508 can be hydrogenated to the corresponding polyamines over a granular Raney cobalt catalyst in the presence of a liquid primary or secondary amine comprised in the feed stream. As amino component which must be present, mention is made of, inter alia, ethylenediamine (EDA) together with numerous further primary or secondary amines.
EP-A 1 209 146 relates to a further process for the continuous hydrogenation of nitrites to primary amines, in which the respective nitrites are reacted in the liquid phase over a suspended, activated Raney catalyst based on an alloy of aluminum and the reaction is carried out in the absence of ammonia and basic alkali metal or alkaline earth metal compounds. Nitrites which can be converted into the corresponding ethylene amines include, among many others, IDAN, EDTN, EDDPN or ethylenediaminemono-propionitrile (EDMPN).
EP-B 0 913 388 relates to a process for the catalytic hydrogenation of nitriles, which comprises contacting of the nitrile with hydrogen in the presence of a cobalt sponge catalyst under conditions for carrying out the conversion of the nitrile group into the primary amine. The cobalt sponge catalyst has been treated beforehand with a catalytic amount of lithium hydroxide and the process is carried out in the presence of water. Suitable nitriles are aliphatic nitriles having from 1 to 30 carbon atoms, including β-amino nitrites such as dimethylaminopropionitrile. A further process for preparing polyamines from the corresponding polynitriles is disclosed in DE-A 27 55 687. In this process, the hydrogenation is carried out over a hydrogenation catalyst in pellet form in the presence of a stabilizer which inhibits decomposition of the catalyst. As polynitrile, it is possible to use, inter alia, ethylenediaminedipropionitrile (EDDPN). A suitable stabilizer is, inter alia, EDA.
US-A 2006/0041170 relates to a process for preparing TETA, in particular TETA salts, and their use as drugs. In this multistage process, EDDN is prepared first. EDDN is subsequently reacted with benzaldehyde to form a (cyclic) imidazolidine derivative. This cyclic compound, which has two cyano groups, is reduced, for example by reaction with hydrogen, to give the corresponding cyclic diamino compound. This diamino compound is in turn hydrolyzed in the presence of an acid to give the corresponding TETA salt. In an alternative embodiment, the cyclic diamino compound is likewise reacted with benzaldehyde to form the corresponding diimino compound which is subsequently again hydrolyzed in the presence of an acid to give the corresponding TETA salt. A further process alternative described in this document is reaction of EDDN with Boc protective groups (tert-butoxycarbonyl groups). The EDDN derivative protected by two Boc protective groups obtained in this way is subsequently hydrogenated to give the corresponding protected TETA derivative. The Bac protective groups are removed by acid hydrolysis to give the corresponding TETA salt. A disadvantage of this process described in US-A 2006/0041170 is, in particular, that it is a multistage hydrogenation process in which the starting material EDDN used firstly has to be chemically converted into a derivative in order to carry out the hydrogenation. A further disadvantage is that TETA is initially obtained as salt and not in the free base form.
Thus, it is disclosed nowhere in the prior art that EDDN or amino nitrite mixtures comprising EDDN and EDMN can be used for the preparation of TETA and, if appropriate, further ethylene amines by direct hydrogenation of the amino nitrite. However, other (industrial) processes for preparing TETA are known.
EP-A 222 934 relates to a process for preparing higher alkylene polyamines by reaction of a vicinal dihaloalkane with an excess of ammonia in the aqueous phase with addition of a strong base, resulting in formation of an imine intermediate which is subsequently reacted with an alkylene polyamine to form the higher alkylene polyamine. A suitable vicinal dihaloalkane is, in particular, ethylene dichloride (EDC or 1,2-dichloroethane). Alkylene polyamines used are, in particular, ethylenediamine or higher ethylene amines such as DETA and also TETA and tetraethylenepentamine (TEPA). In these processes (EDC processes), a mixture of various ethylene amines (linear ethylene amines such as EDA, DETA, TETA, TEPA or higher ethylene amines and cyclic derivatives such as piperazine (Pip) or aminoethylpiperazine (AEPip)) is obtained. Depending on which ethylene amine is added to the starting materials EDC and NH3, the reaction mixture comprises a corresponding proportion of higher ethylene amities. If, for example, TEPA is to be specifically produced, the ethylene amine TETA is added to the starting materials EDC and NH3. As a result, the product (ethylene amine mixture) comprises a higher proportion of TEPA, but also the above-mentioned further linear and cyclic ethylene amines. Disadvantages of this process are, in particular, that the process proceeds with a low selectivity (in respect of the components of the ethylene amine mixture obtained) and that a specific ethylene amine (for example DETA) firstly has to be prepared and is subsequently introduced into the process to produce the next higher ethylene amine (for example TETA) in a targeted manner or to increase the yield. In addition, this process presents a corrosion problem because of the starting materials used (haloalkanes) and the hydrochloric acid formed and also an environmental problem because of the salts formed.
U.S. Pat. No. 3,462,493 relates to a process for preparing TETA, in which an at least five-fold molar excess of EDA is reacted with ethylene dichloride or ethylene dibromide. By-products formed here are, in particular, Pip or piperazinoethylethylenediamine.
DE-T 689 11 508 describes an alternative process for preparing linearly extended polyalkylene polyamines such as TETA. In this process, a bifunctional aliphatic alcohol is reacted with an amine reactant in the presence of a tungsten-comprising catalyst. A suitable bifunctional aliphatic alcohol is, in particular, monoethanolamine (MEA), and EDA or DETA can, for example, be used as amine reactants. This process gives principally mixtures of linearly extended polyalkylene polyamines (i.e. ethylene amine mixtures). These ethylene amine mixtures comprise the ethylene amines DETA, TETA, TEPA, Pip, AEPip or piperazine derivatives of higher ethylene amines, with the proportion of the respective components varying as a function of the amine reactants used. If DETA is used as amine reactant, an ethylene amine mixture having a high proportion of TETA and TEPA is obtained. Disadvantages of this process are that the process proceeds with a low selectivity (in respect of the components of the ethylene amine mixture obtained) and that an additional ethylene amine has to be synthesized first and then reacted with the bifunctional aliphatic alcohol (for example MEA). This forms relatively large amounts of by-products such as aminoethylethanolamine (AEEA) or higher hydroxy-comprising ethylene amines which are of little commercial interest. The relatively large amount of by-products formed is due to MEA or the higher ethanolamines (e.g. AEEA) being able to react with themselves instead of with the amine used. Owing to the (statistically) many possible reactions, the selectivity to the linear TETA is quite low because of the coproducts and cannot be controlled. The synthesis can be carried out only at a partial conversion.
An overview of the preparation of ethylene amines is given by the SRI report “CEH Product Review Ethyleneamines”, SRI International, 2003; pp. 1-53, in which EDA or DETA, in particular, are prepared by processes corresponding to those described above (using the starting materials EDC or MEA). Here, higher ethylene amines such as TETA or TEPA are formed as by-products or are obtained in higher yield by renewed reaction of the starting materials with EDA or DETA.
Furthermore, some processes for preparing EDDN or EDMN have been described in the literature. Thus, K. Masuzawa at al., Bull. Chem. Soc. Japan, volume 41 (1968), pages 702-706, describe a process for the preparation and reaction of nitrogen and sulfur analogues of 2-piperazinone derivatives. The preparation of this class of substances starts out from the starting materials EDA and FACH. The two starting materials are reacted in an equimolar ratio, using methanol as solvent. After the reaction solution has been allowed to stand at room temperature for two days, the solvent and unreacted starting materials are removed under reduced pressure to give an oily product. This oily product comprises a cyclic compound together with EDMN as secondary component. The reaction was carried out with exclusion of water. The oily product is subsequently converted in a multistage process into the desired 2-piperazinone derivatives. This document also describes the preparation of EDDN as an undesirable secondary reaction in the reaction of EDA with FACH. EDDN is obtained if a molar excess of EDA is reacted with FACH in methanol at from 55 to 60° C. After concentrating the reaction mixture under reduced pressure, the product is isolated by vacuum distillation. A yield of about 27.3% based on the EDA used is obtained here.
H. Baganz et al., Chem. Ber, 90 (1957), pages 2944-2949, describe a process for preparing N,N′-ethylenebisamino acid derivatives, with the dihydrochloride of EDDN serving as starting material for this multistage process. This document also describes a synthetic method for the dihydrochloride of EDDN. Here, the dihydrochloride of EDA and potassium cyanide (KCN) are placed in a reaction vessel and 30% strength formaldehyde is subsequently introduced dropwise into the reaction vessel, with the reaction temperature not exceeding 25° C. After a reaction time of 12 hours and addition of sodium hydroxide, the product is shaken with ether, dried and precipitated as ammonium salt by addition of hydrogen chloride. The product obtained is subsequently crystallized. A disadvantage of this process is, in particular, the use of hydrogen chloride and KCN, which give the aqueous phase a high salt content. Furthermore, the extraction with ether is problematical since, owing to the good solubility of EDDN in water, the reaction product does not go completely into the ether phase.
H. Brown et al., Helvetica Chimica Acta, volume 43 (1960), pages 659-666, describe a process for preparing complexing agents of the thiazole series. This multistage process uses EDDN as starting material, and this document also comprises a synthetic method for preparing EDDN. According to the process described therein, EDA and water are placed in a reaction apparatus and HCN and calcium cyanide (Ca(CN)2) in water are subsequently added simultaneously while stirring and cooling in ice. However, no formaldehyde is used in this process. After a complicated work-up, EDDN is obtained in a relatively low yield.
The abovementioned US-A 2006/0041170 likewise comprises methods of preparing the starting material EDDN described therein. Firstly, EDDN can be prepared by direct alkylation of EDA by means of a haloacetonitrile such as chloroacetonitrile or bromoacetonitrile. Secondly, EDDN is prepared by the above-described reaction of EDA, in particular the dihydrochloride of EDA, firstly with formaldehyde and subsequently with cyano salts such as KCN. The reaction product obtained is then treated with an acid. If EDA is used as starting material, it is firstly converted into its salt form, in particular into the dihydrochloride, before being reacted further with formaldehyde. A disadvantage of this process is the salt formation caused by the use of cyano salts. A further disadvantage is the handling of solid EDA salts, since EDA is either used directly as salt or is firstly converted into a salt. In addition, the process described in US-A 2006/0041170 is not suitable for continuous operation.